Displacement measurement method and apparatus, and ultrasonic diagnostic apparatus

ABSTRACT

A displacement measurement apparatus includes an ultrasound sensor transmitting ultrasounds to an object in accordance with a drive signal, and detecting ultrasound echo signals generated in the object to output echo signals; a driving and processing unit supplying the drive signal to the sensor, and processing the echo signals from the sensor to obtain ultrasound echo data; and a controller controlling the driving and processing unit to yield an ultrasound echo data frame at each of plural different temporal phases based on the ultrasound echo data obtained by scanning the object. The ultrasound echo data has one of local single octant spectra, local single quadrant spectra, and local single half-band-sided spectra in a frequency domain. The ultrasound echo data is obtained from plural same bandwidth spectra. A data processing unit calculates a displacement at each local position or distribution thereof in at least one of axial, lateral, and elevational directions by solving simultaneous equations derived at each local position via implementing a predetermined displacement measurement method on the ultrasound echo data yielded at the plural different temporal phases with respect to at least one of the axial, lateral, and elevational carrier frequencies and the phase, or the one of the local single octant spectra, the local single quadrant spectra, and the local single half-band-sided spectra.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional application of U.S. applicationSer. No. 14/591,777, filed on Jan. 7, 2015, which is a Divisionalapplication of U.S. application Ser. No. 12/833,072, filed on Jul. 9,2010, and which claims priority from. Japanese Patent Application Nos.2009-209656, filed on Sep. 10, 2009, and 2010-144921, filed on Jun. 25,2010. The contents of all of the above-identified applications areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention describes displacement measurement methods anddisplacement measurement equipments that allow non-destructive andquantitative measurements of internal mechanical properties or internalphysical quantities such as a displacement, a strain, a velocity, anacceleration etc. in various objects, structures, substances, materials,living tissues etc. For instance, the present invention includes methodsand equipments that generate an ultrasound echo by performing a properbeamforming such that at least one internal distribution of adisplacement vector, a strain tensor, a strain rate tensor, a velocityvector and an acceleration vector can be measured. Such physicalquantities are generated by a mechanical source such as an externalpressure, an external vibration, a radiation force etc. The methods andequipments can also deal with tissues that move spontaneously such as aheart and a lung etc. or moved by a body motion, a respiratory, a heartmotion, a pulsation etc. Also those can also deal with a blood flow in aheart or a blood vessel. A contrast medium can also be used.Simultaneous measurements of such a tissue motion and a blood flow canalso be performed. The results measured can be applied widely, forinstance, to measurements of mechanical properties and thermalproperties.

A medical field is a typical field to which the present invention isapplied, such as ultrasonic diagnosis equipments, magnetic resonanceimaging equipments, optical diagnosis equipments etc. and radiotherapies etc. That is, for instance, deformability and motion-abilityof tissues and blood can be examined for diagnoses. Otherwise, byperforming a tracking of a target tissue motion, the safety, reliabilityand efficiency of various treatments can be increased. Degeneration canalso be monitored for confirming a treatment effectiveness of a regionof interest (ROI). Application of the present invention is not limitedto these. For instance, as non-destructive measurement methods, theevaluations, examinations and diagnoses can be performed for variousobjects.

Description of a Related Art

For instance, in a medical field, treatments of diseases are performedby a radiotherapy, applications of a high intensity focus ultrasound, aleaser, an electromagnetic radio frequency wave or a microwave, acryotherapy, or a cooling therapy etc. In these cases, anabove-mentioned tracking and a non-invasive monitoring of the treatmenteffectiveness can be performed. Also an effectiveness of a medicine suchas an anti-cancer drug can be performed non-invasively. For instance,the treatment effectiveness can be monitored by non-invasively measuringthe degeneration and temperature change generated by radiotherapies.Otherwise, the observation of blood flow in a lesion allows thedifferentiation of the progress of disease. In order to perform adiagnosis and observe a treatment effectiveness, a tissuecharacterization can also be performed by evaluating an elastic constantetc. after the measurements of displacement, strain and their spatialand temporal changes etc. generated by forces applied in a lesion and atreated part.

It is well known that the temperature of a tissue has correlations withthe elastic constants, visco-elastic constants, a delay time and arelaxation time with respect the constants, a density etc. Then, byperforming non-destructive measurements of elastic constants such as ashear modulus and a bulk-modulus etc., visco-elastic constants such as avisco-shear modulus and a visco-bulk modulus etc., a time delay and arelaxation time with respect the moduli, a density etc., the temperatureof a point of interest (POI) and the temperature distribution in an ROIcan be measured. The temperature can also be estimated from the strainsmeasured generated by a temperature change. Such temperaturemeasurements allow the monitoring of thermal treatments and theprediction of a temperature distribution to be generated for a planningof the thermal treatments.

An ultrasound diagnosis equipment used in a medical field uses anultrasound transducer for transmitting an ultrasound into a tissue andreceiving ultrasound echo signals generated in the tissue by areflection or scattering. The received echo signals are converted intoan ultrasound image observable, which exhibits a distribution oftissues. Then, the measurements of tissue displacement (vector)generated by an arbitrary mechanical source, tissue strain (tensor)generated, elastic constants etc. using such an equipment allows thenon-invasive observation of the differences between a lesion and anormal tissue.

At past, for the displacement distribution measurement, the change ofecho signals obtained by transmitting ultrasound at different phases(plural phases or times) is observed. From the measured displacement,the strains etc. is estimated. Concretely, it is proposed that three,two or one-dimensional ROI is set in a target tissue, and a distributionof three, two or one component of a three dimensional displacementvector is measured. Then, elastic constants etc. in ROIs are evaluatedfrom the measured displacements, strains etc.

The transducer is a sensor of a displacement or strain measurement.Instead of the ultrasound transducer, other known transducers such aselectromagnetic sensors, light sensors, laser sensors can also be used.The sensor is a contact type or non-contact type. For a mechanicalsource that yields a displacement or a deformation, the ultrasoundtransducer itself can also be used as a static compressor. Thetransducer can also be used as a vibrator by assembling a mechanicalvibration function into the transducer contact surface. Also others fromthe transducer, a compressor or a vibrator can be used. A heart motionor a pulsation can also be used (i.e., internal mechanical sources).Also a radiated ultrasound or vibration from a transducer can be used asa mechanical source to yield a deformation in an ROI. The transducer canwork as a sensor as well. For the tissue characterization, change inelastic constants, temperatures, thermal properties etc. generated by atreatment can also be used.

However, in the most classical fashion, a tissue displacement ismeasured by applying a one-dimensional signal processing to theultrasound echo signals under the assumption that the target tissuemoves in the same direction as that of the ultrasound beam. Therefore,when the target tissue displacement (motion) has a lateral component(component of the orthogonal direction to the beam direction), themeasurement accuracy of the beam direction (axial direction) becomes low(ref. 1: C. Sumi et al, “Phantom experiment on estimation of shearmodulus distribution in soft tissue from ultrasonic measurement ofdisplacement vector field”, IEICE Trans. on Fundamental, vol. E78-A, no.12, pp. 1655-1664, December 1995). Here, the ultrasound echo signalsinvolve a raw echo signal, an analytic signal, a quadrate detection, andan envelope detection etc. It is also impossible to measure the lateraldisplacement component. Therefore, there exists a limitation for themeasurement accuracy of the blood flow in a heart and a blood vesselrunning parallel to the body surface. In addition, it is also difficultto deal with a part of which deformation cannot be controlled externallyand a tissue deforms spontaneously by the internal mechanical sourcessuch as a heart etc. (for instance, a liver).

Alternatively, the present inventor proposes a displacement vectormeasurement method that yields the vector measurement from the gradientof the phase of local multidimensional (three- or two-dimensional)cross-spectrum of echo signals (multidimensional cross-spectrum phasegradient method). The cross-correlation method can also be used (refs. 1and 2: C. Sumi, “Fine elasticity imaging on utilizing the iterativerf-echo phase matching method,” IEEE Trans. on Ultrasonics,Ferroelectrics and Frequency Control, vol. 46, no. 1, pp. 158-166,January 1999, etc.). The present inventor also propose amultidimensional autocorrelation method and multidimensional Dopplermethod that deal with multidimensional analytic signals (ref. 3: C.Sumi, “Digital measurement method of tissue displacement vector frominstantaneous phase of ultrasonic echo signal,” Technical report ofJapan Society of Ultrasound Medicine, pp. 37-40, December 2002, Tokyo,Japan (in Japanese) or C. Sumi, “Displacement vector measurement usinginstantaneous ultrasound signal phase—Multidimensional autocorrelationand Doppler methods,” IEEE Trans. on Ultrasonics, Ferroelectrics andFrequency Control, vol. 55, pp. 24-43, January 2008, etc.). Thesemeasurement methods are properly used or properly combined according tothe application of the measurement, specifically, according to themeasurement accuracy and calculation time required.

For the displacement vector measurement, the multidimensional phasematching method which the present inventor previously invented iseffective (refs. 1 to 3). The phase matching is performed in amultidimensional space (a three-dimensional space is expressed usingaxial, lateral and elevation directions; a two-dimensional region isexpressed using axial and lateral directions) for the same paired echosignals by rotating a phase of the 1st or 2nd echo signals in ananalogue manner using the measured displacements, or by spatiallyshifting the local echo signals using the approximated displacementcomponents as a multiplication of the corresponding sampling intervalsby truncating or round off. The phase matching prevents the measurementfrom suffering an aliasing due to a large displacement in a beamdirection. Also the phase matching increases a measurement accuracy ofall the displacement components (i.e. all directions) by increasing acorrelation and/or coherence between the echo signals. For instance,coarse measurements obtained by the multidimensional cross-correlationmethod or the multidimensional cross-spectrum phase gradient method areused to perform a coarse phase matching. After the coarse phasematching, the multidimensional cross-spectrum phase gradient method, themultidimensional autocorrelation method or the multidimensional Dopplermethod is used to yield a fine measurement. Otherwise, after the coarsephase matching, the corresponding one-dimensional methods can also beapplied to yield only an axial displacement measurement or adisplacement vector components, although the measurement accuracy islower than that obtained by the multidimensional methods (ref. 3).

By performing the phase matching, even if an uncontrollable mechanicalsource exists in an ROI (heart motion, respiratory, blood vesselpulsation, body motion etc.), it is also possible to measure adisplacement vector or an axial displacement. Thus, the phase matchingallows yielding the useful measurement absolutely. The multidimensionalvector measurement methods also yield results in a real-time similarlyto the corresponding one-dimensional methods.

However, even if the phase matching is performed, the measurementaccuracy of the axial displacement becomes low when using theone-dimensional displacement measurement method. This is because theresidual lateral displacement exists. Thus, the measurement accuracydepends on the accuracy of the coarse phase matching. When using aconventional ultrasound equipment for the displacement vectormeasurement, the accuracy and spatial resolution of the measured lateraldisplacement are low, because the lateral carrier frequency does notexist and the lateral bandwidth is smaller than the axial one. Thus, themeasurement accuracy of a displacement vector and a strain tensorbecomes low, being dependent of the measurement accuracy of the lateraldisplacement.

Then, the present inventor realized a remarkably accurate displacementvector measurement on the basis of the above-mentioned displacementvector measurement methods, however, with a use of echo signals havinglateral and elevational carrier frequencies. Such a use of echo signalsallows the increase in a measurement accuracy of an axial displacement.It is referred to as a lateral modulation we called (refs. 3 and 4: C.Sumi et al, “Effective lateral modulations with applications to shearmodulus reconstruction using displacement vector measurement,” IEEETrans. on Ultrasonics, Ferroelectrics and Frequency Control, vol. 55,pp. 2607-2625, December 2008; ref. 5: C. Sumi et al, “Comparison ofparabolic and Gaussian lateral cosine modulations in ultrasound imaging,displacement vector measurement, and elasticity measurement”, Jpn, J.Appl. Phys., vol. 47(5B), pp. 4137-4144, May 2008 etc.). For the lateralmodulation, J. A. Jensen et al and M. E. Anderson determined anapodization function to be used using the Fraunhofer approximation (ref.6: J. A. Jensen, “A new method for estimation of velocity vectors”, IEEETrans. Ultrason., Ferroelect., Freq. Contr., vol. 45, pp. 837-851, 1998;ref. 7: M. E. Anderson, “multi-dimensional velocity estimation withultrasound using spatial quadrature”, IEEE Trans. Ultrason.,Ferroelect., Freq. Contr., vol. 45, pp. 852-861, 1998), whereas thepresent inventor determines the apodization function using theoptimization method developed (ref. 8: C. Sumi et al, “A demonstrationof optimal apodization determination for proper lateral modulation”,Jpn, J. Appl. Phys., vol. 48(7B), July 2009, etc.).

For the beamforming of a lateral modulation, the present inventorrealized various useful methods on the basis the use of crossed, steeredbeams (i.e., not the Fraunhofer approximation, ref. 4): using aclassical monostatic or multistatic synthetic aperture (SA) method;transmitting crossed beams simultaneously and receiving crossed beamssimultaneously; transmitting crossed plane beams for a wide region andsuperposing generated echo beams; using such crossed beams, however,transmitted or received using different or plural physical apertures;using such crossed beams, however, generated at different phases.

The lateral modulation developed by the present inventor can be realizedby achieving crossed beams using steered beams in arbitrary directions.Then, arbitrary type transducers such as a linear array type transducercan be used, i.e., arbitrary coordinate systems can be used. In suchcoordinate systems, crossed beams can be generated using steered beamshaving arbitrary directions. Thus, the crossed beams are not alwayssymmetric in a lateral direction. Such a non-symmetric beamforming iseffective when the obstacles such as a bone exist, for instance.Non-steered beam can also be used as one beam of crossed beams.Mechanical steering can also be used together. At a point of interest(POI), a steering angle or crossed angle of steered beams should belarge. Although the lateral modulation can be performed with aconsideration about the apodization (beam shape), the apodizationoptimized by the present inventor allows yielding a lateral modulationwith a wide lateral bandwidth. This increases the spatial resolution ofultrasound image obtained and the measurement accuracy of a displacementvector measurement achieved.

For the lateral modulation (ref. 3), to obtain a three-dimensional echodata frame (i.e., three-dimensional displacement vector measurement),crossed beams must be generated using four or three steered beams,whereas to obtain two-dimensional echo data frame (i.e., two-dimensionaldisplacement vector measurement), crossed beams must be generated usingtwo steered beams. In the present invention, similarly to a conventionalcase, the respective three- or two-dimensional frames generated areapproximated as echo data frames that exhibit a tissue distribution atrespective time phases, although it takes a finite time to receive allecho signals and generate the respective frames. The inversion of thetime difference between the frames obtained is called as a frame rate.Due to the existence of a tissue motion, the time required to generateone frame should be short. Hereafter, the time phase is referred to asdefined here.

For the lateral modulation, however, larger number of beams must begenerated than the conventional beamforming. Then, it may take a longertime to obtain echo signals and achieve the signal processing such asthe apodization, switching, implementation of delay on echo signals,phase matching on echo signals, summation of echo signals. Then, theframe late may become lower than the conventional imaging. When using aclassical synthetic aperture (SA), the echo signal-to-noise ratio (SNR)obtained will be low, because the transmitted ultrasound powers from therespective elements are small. In addition, particularly when dealingwith deeply situated tissues, a larger physical aperture is requiredthan that for a conventional beamforming. The field of vision (FOV)obtained may become smaller in lateral and elevational directions thanthat for a conventional beamforming.

Alternatively, an accurate displacement vector measurement can beachieved by synthesizing the accurately measured axial displacementsobtained from respective steered beams with the same steering angle(ref. 3), i.e., the superposition is not performed. However, the framerate may become low similarly to the lateral modulation. When usingsteered beams obtained at different phases, the tissue displacementbetween the two frames obtained leads to a measurement error.

SUMMARY OF THE INVENTION

The purpose of the present invention is that an accurate real-timemeasurement of a displacement vector or a one-directional displacementis achieved on the basis of the proper beamforming that require a shorttime for obtaining one echo data frame without suffering affections by atissue motion.

In order to achieve the above-mentioned purpose, a displacementmeasurement method according to one aspect of the present inventionincludes the steps of:

(a) yielding ultrasound echo data frames by scanning an object laterallyor elevationally using an ultrasound beam steered electrically and/ormechanically with a single steering angle over an arbitrarythree-dimensional orthogonal coordinate system involving existence ofthree axes of a depth direction, a lateral direction, and an elevationaldirection or an arbitrary two-dimensional orthogonal coordinate systeminvolving existence of two axes of a depth direction and a lateraldirection; and

(b) calculating a displacement vector distribution by implementing apredetermined block matching on the ultrasound echo data frames yieldedat more than two phases.

Further, a displacement measurement apparatus according to one aspect ofthe present invention includes:

at least one ultrasound sensor for transmitting ultrasounds to an objectin accordance with at least one drive signal, and detecting ultrasoundecho signals generated in the object to output echo signals;

driving and processing means for supplying the at least one drive signalto the sensor, and processing the echo signals outputted from thesensor;

control means for controlling respective means to yield ultrasound echodata frames by scanning an object laterally or elevationally using anultrasound beam steered electrically and/or mechanically with a singlesteering angle over an arbitrary three-dimensional orthogonal coordinatesystem involving existence of three axes of a depth direction, lateraldirection, and an elevational direction or an arbitrary two-dimensionalorthogonal coordinate system involving existence of two axes of a depthdirection and a lateral direction; and

data processing means for calculating a displacement vector distributionby implementing a predetermined block matching on the ultrasound echodata frames yielded at more than two phases.

The beamforming method according to one aspect of the present inventionuses conventional apodization, switching, delay, phase matching,summation and mechanical scanning etc., by which so-called steeringbeams to be used for scanning the object or target are generated foryielding the echo data frames, however, with the same steering angle(i.e., a single steering angle), for both the transmission and receptionover the three-, two- or lateral one-dimensional region of interest(ROI) constructed. By using displacement vector measurement methods,one-directional displacement measurement methods or the combination, adisplacement vector, a lateral displacement (one-directionaldisplacement) or the distribution is measured on the basis of the phasedifference between the steering beams or echo data frames obtained atdifferent phases. A synthetic aperture can also be used. Theone-dimensional ROI is not always lateral, for instance, an axialone-dimensional ROI.

Because the beamforming method does not generate plural steering beamswith different steering angles, the beamforming allows the decrease inthe errors generated due to the tissue motion during an echo dataacquisition. As described later, however, the beamforming does notalways yield the most accurate measurement and imaging. Then, thelateral modulation described above and the conventional beamforming(non-steering) can also be chosen as a beamforming method together witha displacement measurement method. As described later, a mechanical scancan also be performed. When performing the displacement measurementafter one of the beamformings, as described later, the coordinate systemcan be rotated to increase the measurement accuracy. In a frequencydomain, as described later, spectra division or frequency divisionreferred to as can also be performed. The ultrasound apparatus relatedto the present invention is equipped with such beamformings,displacement measurement methods and function for automatically ormanually choosing or combining the beamformings and displacementmeasurement methods. A synthetic aperture can also be performed.

Thus, on the basis of one of viewpoints of the present invention, thecombinational use of the prescribed steering beams with a singlesteering angle (the same steering angle), and the prescribed processingsand displacement measurement methods allows providing new real-timemeasurement methods for a displacement vector, a lateral displacement(one-directional displacement) and the distribution, new displacementmeasurement apparatuses and new ultrasound diagnosis apparatuses. Asynthetic aperture can also be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a global frame ofdisplacement vector measurement apparatus, related to one of conductforms of the present invention;

FIG. 2 shows an illustration of mechanical scan movements of adisplacement/strain sensor;

FIG. 3 shows illustrations of compositions for beamforming such as anapodization, a switching, a delay, a phase matching, and a summationprocessing etc.;

FIG. 4 shows an illustration of a displacement/strain sensor applicableto the present invention;

FIG. 5 shows an illustration of a lateral scan using steering beams witha single steering angle (the same steering angle);

FIG. 6 shows an illustration of a case of beam steering using amechanical scan;

FIG. 7 shows (a) two-dimensional and (b) three-dimensional spectra for alateral scan using steering beams with a single steering angle as showin FIG. 5;

FIG. 8 shows for two-dimensional region of interest (ROI), illustrationsof (a) crossed, steering beams for a lateral modulation and (b) thecorresponding spectra;

FIG. 9 shows illustrations of (a) a local rigid motion in atwo-dimensional ROI and (b) a displacement of a point;

FIG. 10 shows an illustration for measuring blood flow in a blood vesselrunning parallel to the body surface using electrically or mechanicallysteered beams under the condition of setting a lateral axis of acoordinate system such that the lateral axis corresponds to thedirection of the target displacement;

FIG. 11 shows illustrations for a two-dimensional case, (a) mirrorsetting in a frequency domain, and mirror setting in a spatial domainfor (b) axial and (c) lateral directions;

FIG. 12 shows illustrations for virtual sources as follows, (a) a knownvirtual source that is realized at a focus position of beamforming usinga physical aperture or array elements, (b) a known virtual source thatgains a transmission power and a virtual receiver, and (c) and (d)virtual sources that are realized regardless the position of a focus ofbeamforming using a physical aperture or array elements, specifically,(c) a virtual source for regenerations of an arbitrary vision of field(VOF) and an arbitrary beam direction and (d) a virtual source realizedby scatters;

FIG. 13 shows illustrations for explaining (a) an aliasing generatedwhen a steering angle is made large to increase a lateral carrierfrequency under the condition that a beam pitch is coarse, (b) filteringin a frequency domain of the side lobes and grating lobes that grow whenmaking the steering angle large, and (c) method for obtaining a higherlateral carrier frequency than the Nyquist frequency by making thesteering angle large, i.e., widening a lateral bandwidth by padding zerospectra in higher frequencies than the Nyquist frequency (interpolationsof lateral sampling points of a coordinate system);

FIG. 14 shows illustrations for explaining a rotation of a coordinatesystem for an echo data frame obtained or to be obtained, i.e., arotation after beamforming or at beamforming, and (b) the rotation ofthe coordinate system in a frequency domain.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is explanation in detail of conduct forms of the presentinvention with referring to figures.

FIG. 1 shows a schematic representation of a global frame of adisplacement measurement apparatus, related to one of conduct forms ofthe present invention. This apparatus measures distributions or timeseries of displacement vector components, strain tensor components andtheir temporal and/or spatial partial derivatives etc. in a three-, two-or lateral one-dimensional ROI 7 set in a measurement object 6 to obtainvelocity vector field, acceleration vector field, strain tensor field,strain rate tensor field etc. The one-dimensional ROI is not alwayslateral, for instance, an axial one-dimensional ROI. From thesemeasurements, this apparatus measures following constant distributions,i.e., elastic constants such as shear modulus, Poisson's ratio etc.,visco-elastic constants such as visco-shear modulus, visco-bulk modulusetc., delay times or relaxation times relating these elastic constantsand visco-elastic constants, density etc. Using this apparatus,displacement measurement related to one of conduct forms of the presentinvention is performed. Moreover, using this apparatus, an ultrasounddiagnosis apparatus related to one of conduct forms of the presentinvention is realized.

As shown in FIG. 1, the displacement/strain sensor 5 is directlycontacted to the object surface, or a suitable medium is put between thesensor and object. For this conduct form, as the displacement/strainsensor, an ultrasound transducer is used. The transducer may have one-or two-dimensional array of oscillators etc. A single oscillator canalso be used. One or plural ultrasound sensors transmit ultrasounds tothe object in accordance with one or plural drive signals, and detectultrasound echo signals generated in the object to output one or pluralreceived echo signals. The transmission beamforming processing forms atransmission ultrasound beam using the ultrasounds transmitted from oneor plural ultrasound sensors, whereas the reception beamformingprocessing forms a reception ultrasound beam using the ultrasoundsreceived by one or plural ultrasound sensors.

The displacement between the displacement/strain sensor 5 and the object6 can be mechanically controlled using a position controller 4.Moreover, the relative distance between the displacement/strain sensor 5and the object 6 can be mechanically controlled by a position controller4′. An ultrasound transmitter or an ultrasound pulser 5′ is equippedwith to generate one or plural drive signals to drive thedisplacement/strain sensor 5, and 5′ also serves as an outputcontroller, i.e., a receiver with an amplifier of one or plural echosignals detected by the displacement/strain sensor 5. Thus, 5′ is adrive/output controller. Furthermore, mechanical sources 8 and 8′ can beequipped with to actively apply static compressions and vibrations,respectively, together with a mechanical position controller 4″. For themechanical source, the ultrasound sensor can also be as a compressor orvibrator. A heart motion and a pulsation can also be used as amechanical source 8″.

The echo signals output from the drive/output controller 5′ are storedat a data storage 2 through a measurement controller 3. Therefore, thedrive/output controller 5′ may have an analogue-to-digital (AD)converter inside or outside. As described specifically later, thedrive/output controller 5′ can also perform a reception beamforming aswell as a transmission beamforming. Then, an ultrasound echo data framegenerated by the reception beamforming may be stored at the data storage2. Otherwise, the plural received echo signals before performing areception beamforming may be stored at the data storage 2, after whichthe stored data are read out by a data processing unit 1. The dataprocessing unit may also perform the reception beamforming, by which anecho data frame may be generated. In this case, the echo data framegenerated can be stored at the data storage 2 through the measurementcontroller 3. For both cases, the command for the displacementmeasurement is output from the measurement controller 3, displacementvector component distributions or one-directional displacementdistribution in an ROI 7 of an arbitrary time, or their time series arecalculated from plural echo data frames generated at different phasesusing the calculation processing described specifically later. Thus, inthe former case, the data processing unit 1 performs the displacementcalculations after reading out the echo data frames from the datastorage 2, whereas in the latter case, the generation of echo dataframes (i.e., beamforming) and the displacement calculations can also beperformed by the respective processors. The distributions ofdisplacement vector components or one-directional displacement, or theirtime series calculated may be stored at the data storage 2.

The data processing unit 1 calculates the temporal and/or spatialpartial derivatives of the displacement component distributionsmeasured, i.e., strain tensor component distributions (time series),strain rate tensor component distributions (time series), velocityvector component distributions (time series), acceleration vectorcomponent distributions (time series). That is, the strain tensorcomponent distributions (time series) are calculated by implementing a3D, 2D or 1D spatial differential filter to the displacement vectorcomponent distributions (time series) obtained. The cut off frequenciesof all the filters can be set different values freely at each point andtime in each spatial and temporal direction as those of usual filters.The acceleration vector component distributions (time series) arecalculated by implementing a time differential filter twice to themeasured displacement vector component distributions (time series). Thestrain rate tensor component distributions (time series) are calculatedby implementing a spatial differential filter to the velocity vectorcomponent distributions (time series) calculated by implementing a timedifferential filter to the displacement vector component distributions(time series) obtained, or by implementing a time differential filteronce to the strain tensor component distributions (time series)obtained. Moreover, when strain tensor component distributions (timeseries) are directly calculated of the ROI 7 and obtained, strain ratetensor component distributions (times series) are obtained byimplementing time differential filter to the measured strain tensorcomponent distributions (time series).

Furthermore, this data processor 1 calculates following constantdistributions, i.e., elastic constants such as shear modulus, Poisson'sratio etc., visco-elastic constants such as vis co-shear modulus,visco-bulk modulus etc., delay times or relaxation times relating theseelastic constants and visco-elastic constants or density from thecalculated distributions of strain tensor components (time series),strain rate tensor components (time series), acceleration vectorcomponents (time series) etc. These calculated results are stored at thestorage 2.

The measurement controller 3 controls the data processing unit 1, theposition controllers 4 and 4″, and the drive/output controller 5′. Theposition controllers 4 and 4′ may be a human hand. When the object 6 isspatially fixed, the position controller 4′ is not used. When thedisplacement/strain sensor 5 is an electric scan type, the positioncontroller 4 is not always used. Being dependent of the size of the ROI7, it may be possible to achieve the measurements without mechanicalscanning. The displacement (strain) sensor 5 may be contacted onto theobject 6 directly, or may not. For instance, when monitoring thetreatment effectiveness of High Intensity Focus Ultrasound (HIFU), thedisplacement/strain sensor 5 and the object 6′ may be dipped in orimmersed in a water tank.

FIG. 2 shows an illustration for explaining the mechanical scan usingthe displacement/strain sensor 5. The mechanical scan includes amechanical steering. The position controller 4 shown in FIG. 1 controlsthe relative position between the displacement/strain sensor 5 and theobject 6 mechanically. For instance, as shown in FIG. 2, the positioncontroller 4 realizes vertical, horizontal, turn and fan-directionalmovements. Then, the position controller may by a human hand.

As shown in FIG. 1, the output of the drive/output controller 5′ isstored at the data storage 2 successively or with a prescribed interval.The data processing unit 1 controls the drive/output controller 5′ andthen acquires the echo's basic wave components, n-th harmonic wavecomponents (n from 2 to N) or all the components in three-, two- orone-dimensional ROI 7, and implements the calculation processingdescribed later to yield displacement data, strain data, strain ratedata or acceleration data.

As described above, the drive/output controller 5′ and the dataprocessing unit 1 obey the commands of the measurement controller 3 toperform the beamforming such as transmission fixed focusing,multi-transmission fixed focusing, reception dynamic focusing etc.Furthermore, an apodization is also performed to sharpen the ultrasoundbeam, i.e., weighting the ultrasounds transmitted and received at therespective sensors. If necessary, with the steering of the beams, theecho signals from the ROI 7 are acquired.

FIG. 3 shows illustrations of compositions for beamforming such as anapodization, a switching, a delay, a phase matching, and a summationprocessing etc. The order of the connections are changeable. Forinstance, in the case of FIG. 3, the respective oscillators or sensors 5a assembled in the displacement/strain senor 5 is connected to delaylines 11 and amplifiers etc. The delay lines are connected toapodization units or switches 12. The apodization units are comprised ofamplifiers and attenuators etc., whereas the switches make therespective channels on or off. The delay lines 11, and apodization unitsor switches 12 are controlled by the measurement controller 3 (FIG. 1).The plural apodization units or switches 12 are connected to thesummation unit 13.

For the reception of the echo signals, plural echo signals outputthrough the plural sensors 5 a, amplifiers, delay lines 11 andapodization units (a kind of calculator can also be used) or switches 12etc. are properly summed by the summation unit 13, by which thereception-focused beams are obtained. The echo data frames are obtainedby A/D conversion of the echo signals using the A/D converter. For thetransmission of ultrasounds, the drive signals are supplied to theplural sensors 5 a through the apodization units or switches 12, delaylines 11, amplifiers etc. All these components may also be realized bythe data processing unit 1 or partially by the drive/output controller5; and the order of the connections and the comprising can also bearranged variously.

For this conduct form, the beam steering with a single steering angle(the same steering angle) is performed. The object 6 is scanned in alateral direction. However, it is not always that the steering angle isinvariant. If possible, the steering angle and crossed angle should beas large as possible. The combinational use of the single aperture andmechanical scan and synthetic aperture can also be performed. For allthe beamforming, the received echo signals are properly filtered,amplified and A/D-converted. If necessary, the calculator can also bewidely used for the signal processing.

FIG. 4 shows an illustration of a displacement/strain sensor 5applicable to the present invention. For this invention, as thedisplacement/strain sensor 5, the following type ultrasound transducerscan be utilized, i.e., a two-dimensional array type being mechanicalscan possible, a two-dimensional array type being electronic scanpossible, a one-dimensional array type being mechanical scan possible,and a one-dimensional array type being electronic scan possible. Othervarious type transducer such as a sector-type transducer can also beused. To increase the steering angle, a mechanical scan can also beperformed.

FIG. 5 shows an illustration of a lateral scan using steering beams witha single steering angle (the same steering angle), in which θ expressesthe steering angle (0°<θ<90°). FIG. 5a shows a scan of a two-dimensionalregion using a one-dimensional array, whereas FIG. 5b shows a scan of athree-dimensional region using a two-dimensional array. FIG. 6 shows amechanical steering, in which θm shows the steering angle (0°<θm<90°).When generating the echo data frame or after generating the frame, aproper three-dimensional orthogonal coordinate system involving theexistence of three axes of a depth direction, and the lateral andelevational directions or a proper two-dimensional orthogonal coordinatesystem involving the existence of two axes of a depth direction and thelateral direction is formed.

For this conduct form, the beam steering with a steering angle isperformed as described in paragraphs 0035 to 0037 (FIG. 5). As describedin the paragraphs 0035 to 0037, the beam steering can be performed usingthe electric beamforming such as the apodization, switching, delay,phase matching, summation processing etc. Also as described in theparagraph 0033, the mechanical scan (FIGS. 2 and 6) can also beperformed by slanting the displacement/strain sensor 5. A syntheticaperture can also be performed.

For the case using the electric steering, when generating the steeringbeams, an arbitrary three-dimensional orthogonal coordinate systeminvolving the existence of three axes of a depth direction, and thelateral and elevational directions or an arbitrary two-dimensionalorthogonal coordinate system involving the existence of two axes of adepth direction and the lateral direction is formed. When the targettissue moves in a lateral direction dominantly, not a displacementvector measurement but a one-dimensional displacement measurementdescribed specifically later is also applicable. In such a case, inorder to increase the measurement accuracy, the coordinate system is setsuch that not an axial direction but a lateral direction corresponds tothe direction of the target motion. In such a case, the mechanical scanmay also be performed by slanting the displacement/strain sensor 5. Sucha lateral one-dimensional displacement measurement does not lead to themeasurement errors (described above) caused when using the conventionalaxial one-dimensional displacement measurement used under the conditionthat the beam direction cannot set in the direction of the targetmotion. Similarly to the lateral modulation (LM), the configurations ofthe displacement/strain sensor 5 and the object become simple and themeasurement accuracy achieved also becomes high. When the target tissuedominantly moves in the depth direction, the one-dimensionaldisplacement measurement should be performed under the condition thatthe beam direction corresponds to the depth direction. That is, eitheraxial or lateral axis should be chosen such that easily the axis can beset in such a proper way. The beam steering should be performed suchthat the beam is steered in the direction of the target motion. Then, ifnecessary, the mechanical scan may also be performed by slanting thedisplacement/strain sensor 5. However, the one-dimensional displacementmeasurement should used for the measurement of a lateral displacement. Asynthetic aperture may also be performed. Although the one-dimensionaldisplacement measurement is referred to as using “one-dimensional,” asis well known, multidimensional signal processings are used forstabilizing the measurement and increasing the measurement accuracy, forinstance, for a moving-average of a phase difference etc. The“One-dimension” means the dimension of the target displacement, i.e.,one-direction. The one-dimensional displacement measurement can also bereferred to as the one-directional displacement measurement.

When performing the mechanical beam steering, the displacement/strainsensor 5 is slanted with respect to the object by the mechanicalscanning (FIG. 6). In such a case, the mechanical steering angle δmshown in FIG. 6 is sensed, which is used for forming a three-dimensionalorthogonal coordinate system involving the existence of three axes of adepth direction, and the lateral and elevational directions or atwo-dimensional orthogonal coordinate system involving the existence oftwo axes of a depth direction and the lateral direction. Alternatively,after beamforming using a three- or two-dimensional orthogonalcoordinate system without using the mechanical steering angle θm, thecoordinate system is rotated using the mechanical steering angle θm suchthat the same coordinate system having an axis of a depth direction atleast (FIG. 6). In such a case, the steered beam data digitized by A/Dconversion are interpolated to obtain the data over the coordinatesystem reformed. A synthetic aperture may also be used together.

In such a case, if the target tissue moves in a lateral directiondominantly, not a displacement vector measurement but a lateralone-dimensional displacement measurement described specifically later isapplicable. In such a case, in order to increase the measurementaccuracy, the coordinate system is set such that not an axial directionbut a lateral direction corresponds to the direction of the targetmotion. When the target tissue dominantly moves in the depth direction,the one-dimensional displacement measurement should be performed underthe condition that the beam direction corresponds to the depthdirection. That is, either axial or lateral axis should be chosen suchthat easily the axis can be set in such a proper way. The beam steeringshould be performed such that the beam is steered in the direction ofthe target motion. Strictly, the interpolation processing should beperformed using the above-described phase matching on the basis of theNyquist theorem (see ref. 1: The value at the desired position isobtained by spatially shifting the echo data by multiplying a complexexponential expressed using the spatial shift to be realized to theFourier's transform of the echo data). However, the other interpolationssuch as the linear interpolation etc. can also be performed as theapproximate interpolations. A synthetic aperture can also be usedtogether.

For the measurement of spatial displacement distributions, the object isscanned using a steering beam with a single steering angle. For thescanning, the direction of the scanning should correspond to that of thelateral direction of the coordinate system to be used finally. It isabsolutely required that every sampling point in the ROI has a steeringangle not equal to zero at least (For the lateral modulation, crossedbeams are required at each point). For instance, when using a convex- orsector-type transducer, a single steering angle should be realized withrespect to the depth direction (axis) of the orthogonal coordinatesystem that is determined by the curvature of the aperture used. Theobject should be scanned in the lateral direction (axis) simultaneouslyset. A synthetic aperture can also be performed. Otherwise, a steeringbeam with a single steering angle is used over an arbitrary orthogonalcoordinate system because an arbitrary shape beam can be tried to besteered in an arbitrary direction within a limitation regardless theaperture geometry by beamforming on the basis the delay, phase matching,summation and apodization or virtual source and receiver describedlater. Generally, the error of the steering angle with respect to thedesired one leads to the measurement error, the displacement measurementmethods used or of the present inventions are robust to such an error.

The data processing unit 1 shown in FIG. 1 implement proper displacementmeasurement methods on the more than two echo data frames obtained bythe beam steering at pre- and post-deformation at least to yield two- orthree-dimensional displacement vector components, one-directionaldisplacement, their distributions or their time series. If necessary,the mirror setting of echo data is also performed as describedspecifically later. For the displacement vector measurement,multidimensional displacement vector measurement methods on the basis ofa block matching can be used, for instance. In such a case, the mirrorsetting is not required. Although the block matching methods can also beused for the measurement of a one-directional displacement,multidimensional displacement vector measurement methods with the mirrorsetting but no block matching yields more accurate measurements.Together with the one-dimensional displacement measurement methods, theone-directional displacement measurement methods described specificallylater can also be used for the one-directional displacement measurement,concretely, lateral one-directional displacement measurement methods.However, these one-dimensional and one-directional measurement methodsyield lower measurement accuracy than the corresponding multidimensionaldisplacement vector measurement methods even though the multidimensionalsignal processing is performed such as a moving average.

The data processing unit 1 can also perform an echo imaging byimplementing the mirror setting on the echo data frame obtained by thebeam steering with a single steering angle. By the processing,quasi-lateral modulation can be performed locally, i.e., superimpositionof the mirrored local echo data. When performing a lateral modulation,the one-dimensional and one-directional displacement measurement methodscan be used by implementing a demodulation. For the demodulation,several methods have been reported, for instance, ref. 9, J. A. Jensen,“A new estimator for vector velocity estimation,” IEEE Trans. Ultrason.,Ferroelect., Freq. Contr., vol. 48, pp. 886-894, 2001; and ref. 10, M.E. Anderson, “A heterodyning demodulation technique for spatialquadrature,” in 2000 IEEE Ultrasonics Symposium etc. With respect tothese, a more simple demodulation method of the present invention willbe described later.

Here, it is recalled that for these measurement methods for themultidimensional displacement vector and one-directional displacementallows the measurements by using the phase of the ultrasound echosignals obtained at more than two phases (i.e., different times).

The data processing unit 1 also calculates strain tensor components,strain rate tensor components, acceleration vector components, velocityvector components, their distributions and their time series byimplementing spatial and temporal differential filters on the measureddisplacement vector components, their distributions and their timeseries.

For the purposes, in order to increase the measurement accuracy of thedisplacement in the scanning direction, the carrier frequency of thescanning direction should be made as large as possible by increasing theabove-described electric and mechanical steering angles, i.e., θ in FIG.5 and θm in FIG. 6, for instance, θ≅45° and θm≅45°, if possible.However, the steering angle may not be large enough because a largesteering angle decreases the SNR of echo signals. Thus, if necessary,the electric steering may performed with the combination of themechanical steering. A synthetic aperture may also be performed.

The carrier frequency of the scanning direction should be large. Inaccordance, the beam pitch should be small such that the aliasing doesnot occur. That is, the carrier frequency cannot become larger than thehighest frequency determined by the beam pitch Δy on the basis of thesampling theorem, i.e., 1/(2Δy). However, by making the electricsteering angle large, the side lobes and grating lobes growsignificantly, all the lobes are tried to be removed in a frequencydomain. A synthetic aperture may also be performed.

However, when it is possible to achieve a higher frequency than thehighest frequency obtained by the beam pitch realized (Nyquist theorem)by making the steering angle large, the data processing unit 1 widens alateral bandwidth by padding zero spectra in higher frequencies than theNyquist frequency (interpolations of lateral sampling points of acoordinate system). In a spatial domain, the number of means can beincreased by the spatial interpolations. At the moment of thebeamforming, the number of beams can also be increased. In contrary,when a high carrier frequency cannot be obtained, the data processingunit can rotate the coordinate system of the echo data frame. However,the beams should be steered in the direction of the target motion.Recall the measurement case of the blood flow (displacement, velocityetc.) in a vessel running parallel to the body surface (FIG. 6). Asynthetic aperture can also be used together.

For the purposes, a fundamental wave, or harmonic waves of which higheraxial carrier frequency and larger lateral bandwidth respectivelyincrease the measurement accuracy of the axial and lateraldisplacements, or all waves of which total single-to-noise ratio may belarger than that of the harmonic wave solo are properly used.

That is, the echo imaging is performed using an ultrasound echo signalitself, a fundamental wave extracted (n=1) solo, one of harmonic wavesextracted (n=2 to N) solo, or combinations of them. Moreover, themeasurement of a displacement vector or a one-directional displacement(mainly, lateral one) is performed.

As described above, the displacement measurement apparatus related tothe present conduct form allows the measurements of displacement vectorcomponents (distributions, time series), a one-directional displacement(distribution, time series), strain tensor components (distributions,time series), strain rate tensor components (distributions, series),acceleration vector components (distributions, series), velocity vectorcomponents (distributions, series) etc. using the ultrasound echo dataframe measured over the three-, two- or lateral one-dimensional ROI inthe object. The apparatus is comprising, the displacement/strain sensor5 (the ultrasound transducer); mechanical controller 4 of relativeposition, and vertical, horizontal, turn and fan-directional movements;the drive/output controller 5′ for generating drive signals to drive thedisplacement/strain sensor as the ultrasound transmitter or theultrasound pulser, processing echo signals detected by thedisplacement/strain sensor as the receiver with an amplifier; thedrive/output controller 5′ or the data processing unit 1 for beamformingsuch as the prescribed beam steering (focusing such as transmissionfixed focusing/reception dynamic focusing, transmission multiplefocusing/reception dynamic focusing; apodization for sharpening the beamshape); the data storage 2 for storing the output of thedisplacement/strain sensor. For the synthetic aperture processing, thedata storage 2 and the data processing unit 1 work mainly after the A/Dconversion.

The data processing unit 1 also works for calculating the displacementvector components (distributions, time series), one-directionaldisplacement (distribution, time series), strain tensor components(distributions, time series), strain rate tensor components(distributions, series), acceleration vector components (distributions,series), velocity vector components (distributions, series) etc.,whereas the data storage 2 also stores the calculated results. For echodata acquisition, a mechanical scan can be combined with the electricsteering.

The data processing unit 1 will also calculate the strain tensorcomponents (distributions, time series) by implementing a 3D, 2D or 1Dspatial differential filter with a cutoff frequency in a spatial domainor their frequency responses to the measured three- or two-dimensionaldisplacement vector components (distributions, time series) in thethree-dimensional ROI, two-dimensional displacement vector components(distributions, time series) in the two-dimensional ROI, one-directionaldisplacement (distribution, time series) in the three-, two- orone-dimensional ROI.

The data processing unit 1 will also calculate the strain rate tensorcomponents (distributions, time series), acceleration vector components(distributions, time series) and velocity vector components(distributions, time series) by implementing the temporal differentialfilter with a cutoff frequency or the frequency response to the measuredtime series.

To generate more than one strain tensor field (or one displacementvector field) in the three-, two- or one-dimensional ROI in the object,the compressor or vibrator can also be used as a mechanical source.Otherwise, the spontaneous tissue motion such as a heart motion, apulsation, a respiratory etc. may also become such a mechanical source.Such strain tensor components (distributions, time series) generated aremeasured.

The displacement/strain sensors (ultrasound transducers) applicable tothe present invention are following types, i.e., the single aperturetype being mechanical scan possible, the two-dimensional array typebeing electronic or mechanical scan possible, the one-dimensional arraytype being electric or mechanical scan possible, and other varioustypes. To increase the steering angle, a mechanical scan can also beperformed. Echo data frames are obtained by performing the prescribedbeam steering using the sensors. A synthetic aperture may also beperformed. The displacement/strain sensor may be contacted onto theobject directly, or may not. In such a case, the contact surface of thesensor serves as a compressor or vibrator as a mechanical source. Whenmonitoring the treatment effectiveness of High Intensity FocusUltrasound (HIFU), the displacement/strain sensor and the object may bedipped in or immersed in a water tank (a non-contact case).

When measuring the elasticity such as strain(s), elastic constantdistribution(s) or visco-elastic constant distribution(s), a suitablemedium is put as a reference for the measurement between the object andthe sensor (mechanical source). Otherwise, such a reference can also beproperly assembled in the sensor.

Thus, by performing the prescribed beam steering using such typedisplacement/strain sensors, the data processing unit calculates three-or two-dimensional displacement vector components (distributions, timeseries) in the three-dimensional ROI, two-dimensional displacementvector components (distributions, time series) in the two-dimensionalROI, or one-directional displacement (distribution, time series) in thethree-, two- or one-dimensional ROI; strain tensor components, strainrate tensor components, acceleration vector components, velocity vectorcomponents, their distributions and their time series.

Moreover, in these case, the data processing unit can also calculate theabove-described displacement vector components (distributions, timeseries), velocity vector components (distributions, time series),acceleration vector components (distributions, time series), straintensor components (distributions, time series), strain rate tensorcomponents (distributions, time series) using the ultrasound echo signalobtained itself, a fundamental wave extracted (n=1) solo, one ofharmonic waves extracted (n=2 to N) solo, or combinations of them.

The following is explanation of the beamforming (i.e., beam steering)and displacement measurement methods used in the drive/output controlleror the data processing unit.

For this conduct form, the beam steering with a steering angle isperformed as described in paragraphs 0035 to 0037 (FIG. 5a ,two-dimensional case; 5 b, three-dimensional case). As described in theparagraphs 0035 to 0037, the beam steering can be performed using theelectric beamforming such as the apodization, switching, delay, phasematching, summation processing etc. Also as described in the paragraph0033 (FIG. 2), the mechanical scan can also be performed by slanting thedisplacement/strain sensor. A synthetic aperture can also be performed.

For the case using the electric steering, when generating the steeringbeams, an arbitrary three-dimensional orthogonal coordinate systeminvolving the existence of three axes of a depth direction, and thelateral and elevational directions or an arbitrary two-dimensionalorthogonal coordinate system involving the existence of two axes of adepth direction and the lateral direction is formed. When the targettissue moves in a lateral direction dominantly, not a displacementvector measurement but a one-dimensional displacement measurementdescribed specifically later is also applicable. In such a case, inorder to increase the measurement accuracy, the coordinate system is setsuch that not an axial direction but a lateral direction corresponds tothe direction of the target motion. In such a case, the mechanical scanmay also be performed by slanting the displacement/strain sensor 5. Whenthe target tissue dominantly moves in the depth direction, theone-dimensional displacement measurement should be performed under thecondition that the beam direction corresponds to the depth direction.That is, either axial or lateral axis should be chosen such that easilythe axis can be set in such a proper way. The beam steering should beperformed such that the beam is steered in the direction of the targetmotion. Then, if necessary, the mechanical scan may also be performed byslanting the displacement/strain sensor 5. However, the one-dimensionaldisplacement measurement should used for the measurement of a lateraldisplacement. A synthetic aperture may also be performed.

When performing the mechanical beam steering, the displacement/strainsensor 5 is slanted with respect to the object by the mechanicalscanning (FIG. 6). In such a case, the mechanical steering angle θmshown in FIG. 6 is sensed, which is used for forming a three-dimensionalorthogonal coordinate system involving the existence of three axes of adepth direction, and the lateral and elevational directions or atwo-dimensional orthogonal coordinate system involving the existence oftwo axes of a depth direction and the lateral direction. Alternatively,after beamforming using a three- or two-dimensional orthogonalcoordinate system without using the mechanical steering angle θm, thecoordinate system is rotated using the mechanical steering angle θm suchthat the same coordinate system having an axis of a depth direction atleast (FIG. 6). In such a case, the steered beam data digitized by A/Dconversion are interpolated to obtain the data over the coordinatesystem reformed. Also in the case of mechanical scan, when the targettissue moves in a lateral direction dominantly, not a displacementvector measurement but a one-dimensional displacement measurementdescribed specifically later is also applicable. In such a case, inorder to increase the measurement accuracy, the coordinate system is setsuch that not an axial direction but a lateral direction corresponds tothe direction of the target motion. When the target tissue dominantlymoves in the depth direction, the one-dimensional displacementmeasurement should be performed under the condition that the beamdirection corresponds to the depth direction. That is, either axial orlateral axis should be chosen such that easily the axis can be set insuch a proper way. The beam steering should be performed such that thebeam is steered in the direction of the target motion. A syntheticaperture may also be used together.

Strictly, the interpolation processing should be performed using theabove-described phase matching on the basis of the Nyquist theorem (seeref. 1: The value at the desired position is obtained by spatiallyshifting the echo data by multiplying a complex exponential expressedusing the spatial shift to be realized to the Fourier's transform of theecho data). However, the other interpolations such as the linearinterpolation etc. can also be performed as the approximateinterpolations. For the measurement of spatial displacementdistributions, the object is scanned using a steering beam with a singlesteering angle. For the scanning, the direction of the scanning shouldcorrespond to that of the lateral direction of the coordinate system tobe used finally. It is absolutely required that every sampling point inthe ROI has a steering angle not equal to zero at least (For the lateralmodulation, crossed beams are required at each point). For instance,when using a convex- or sector-type transducer, a single steering angleshould be realized with respect to the depth direction (axis) of theorthogonal coordinate system that is determined by the curvature of theaperture used. The object should be scanned in the lateral direction(axis) simultaneously set. A synthetic aperture can also be performed.Otherwise, as described above, a steering beam with a single steeringangle is used over an arbitrary orthogonal coordinate system because anarbitrary shape beam can be tried to be steered in an arbitrarydirection within a limitation regardless the aperture geometry bybeamforming on the basis the delay, phase matching, summation andapodization or virtual source and receiver described later. Generally,the error of the steering angle with respect to the desired one leads tothe measurement error, the displacement measurement methods used or ofthe present inventions are robust to such an error.

As the results, for the respective two- and three-dimensional ROIs, asingle quadrant (FIG. 7a ) and a single octant (FIG. 7b ) spectra areobtained. In both frequency domains, the same single spectra existsymmetrically with respect to the origin. The “θ” shown in FIG. 7corresponds to the steering angle “θ” shown in FIG. 5.

The lateral modulation described in the paragraph 0013 can be obtainedin a two-dimensional ROI case by generating the crossed beams in alaterally symmetric condition using the steered beams of the presentinvention as shown in FIG. 8a (ref. 3). Then, when the single spectraobtained by the single steering angle used in the present invent isillustrated in FIG. 7a , that of the lateral modulation is illustratedin FIG. 8b . That is, independent two single quadrant spectra areobtained. In the three-dimensional ROI case, the lateral modulation isequivalent to the crossed three or four steered beams. As the results,three or four octant spectra are obtained in a frequency domain (seeFIG. 1a in ref. 3). According to the measurement accuracy required forthe displacement vector measurement or one-directional displacement, thelateral modulation should also be selected by a switching. Then, thedisplacement measurement apparatus is also equipped with a function thatallows the generation of the symmetric steered beams, i.e., crossedbeams. In such a case, the echo imaging on the basis of the lateralmodulation is also performed. Thus, in such a case, a high spatialresolution can be obtained for the echo imaging in both the axial andlateral directions. A synthetic aperture may also be performed.

For the lateral modulation, the point is that crossed beams must berealized. That is, for an arbitrary coordinate system realized by anarbitrary type transducer, crossed beams must be realized anyway.Non-symmetric crossed beams can also be used with respect to the axis ofa depth direction, if obstacles such as bones exist in the superficialregion. Plural transducers can also be used. The mechanical scan mayalso be performed together. At each position in the ROI, the steeringangle or the angle between the crossed beams should be as large aspossible. In order to control the measurement accuracies of thedisplacement vector components, as described above, the coordinatesystem can be controlled. The coordinate control is describedspecifically later. When using one-dimensional displacement measurementmethods, the symmetric beams obtained by the coordinate rotation aredemodulated as described specifically later.

When performing the lateral modulation, the multidimensionaldisplacement vector can also be measured using the multidimensionaldisplacement vector measurement methods such as the multidimensionalcross-spectrum phase gradient method (MCSPGM, refs. 1 and 2), themultidimensional autocorrelation method (MAM, ref. 3) and themultidimensional Doppler method (MDM, ref. 3).

MCSPGM calculates the local displacement vector between the echo dataframes obtained at two phases (different times) using the local phasecharacteristics under the assumption of a rigid motion. Then, the methodfalls in a category of the block matching method. Specifically, ananalogue displacement vector measurement can be obtained in a frequencydomain by applying the least squares method to the gradient of the localcross-spectrum phase obtained from the digitized two echo data frames.For instance, the measurement of local two displacement components in atwo-dimensional ROI is illustrated in FIG. 9a . Similarly, the localthree displacement vector components can also be measured for thethree-dimensional ROI.

The cross-correlation method and Sum absolute difference (SAD) methodare also block matching methods. These two methods are also used for thecompression of dynamic image data etc. However, for the tissuedisplacement measurement, these two methods yield only displacement dataexpressed by the multiplications of the integers and the samplingintervals in the respective directions. Then, these two methods can beused not for the fine measurements but coarse measurements.

Alternatively, MAM and MDM calculates the two and three displacementvector components at each position in the ROI by solving thesimultaneous equations derived from the two- or three-dimensionalanalytic signals obtained from the respective independent singlequadrant and octant spectra (paragraph 0068) at two phases (differenttimes). For instance, the measurement of two displacement components ata position in a two-dimensional ROI is illustrated in FIG. 9b .Similarly, the three displacement vector components at a position canalso be measured for the three-dimensional ROI. In the case dealing witha three-dimensional displacement vector components, four or threeindependent octant spectra are used, whereas in the case dealing with atwo-dimensional displacement vector components, two independent quadrantspectra are used. Then, occasionally, the least squares method can beused to solve the simultaneous equations.

In the derived equations at each position, the coefficients multipliedto the unknown displacement vector components are instantaneousfrequencies of the echo signal at the position, whereas the constantsare the difference of the instantaneous phases obtained at two phases(different times). To stabilize the displacement vector measurements,the instantaneous frequencies and the difference of the instantaneousphases are calculated with a moving-average. Alternatively, in anotherversion of the MAM and MDM, the assumption of the rigid motion can alsobe used similarly to the MCSPGM. That is, one displacement vector isdealt with for a local region. Then, the least squares method is used tosolve the simultaneous equations derived for the local region in whichnumber of the position is larger than the number of unknown displacementcomponents. Because the MAM and MDM solved in the manner also falls in acategory of a block matching method similarly to the MCSPGM, the MAM andMDM are referred to as MAMb and MDMb. Also for the MAMb and MDMb, thesame moving-average may also be performed to calculate the instantaneousfrequencies and the difference of the instantaneous phases.

The MAMb and MDMb without the calculations using moving-average but theleast squares method solo require fewer calculations. In general,however, a block matching method yields less accuracy in themeasurements of the strains and their spatial distributions as well asthe rigid motion as we clarified. The spatial resolution of thedisplacement vector measurement is determined by the width of themoving-average or the local region size used.

Alternatively, the corresponding one-dimensional or one-directionaldisplacement measurement methods such as one-dimensional Doppler methodhave the almost 50-years history in the no lateral modulation case. Asdescribed above, the beam is tried to be steered in the direction of thetarget motion such that the carrier frequency in the direction of thetarget motion is realized. Correspondingly, we have also theone-dimensional cross-spectrum phase gradient method, autocorrelationmethod, cross-correlation method and SAD.

However, for instance, there is a limitation about the measurementaccuracy achieved although the beam is tried to be steered in thedirection of the blood flow if the blood vessel runs parallel to thebody surface (FIG. 6). It is also difficult to measure the liver motionthat moves and deforms in the lateral direction with a relation to ahear motion. There is also limitation about the accuracy of themeasurement of the complex motion and deformation such as the hearmotion and blood flow in the heart. In such cases, i.e., the target alsomoves in the lateral or elevational direction, the combination of thelateral modulation and multidimensional displacement vector measurementmethods is effective. The combination allows the increase in themeasurement accuracy of the displacement in the depth direction as wellas the lateral displacement measurement. The combination also achievesthe simple manual measurement, i.e., the transducer is only attachedonto the target surface in the neighborhood of the target region.

For the measurements of elasticity and strain of breast and thyroid, thetransducer can be used as a compressor. Then, in such cases, theone-directional displacement measurement methods can also be used.However, if the target tissue moves out of the beams transmitted, themeasurement accuracy degrades. Then, as described in paragraphs 0010 to0011, the multidimensional phase matching method the present inventorinvented previously must also be used together.

Thus, the multidimensional phase matching method also increases themeasurement accuracy of the displacement vector. The multidimensionalphase matching can also be used when the lateral modulation isperformed. Although in such a case, the demodulation methods describedin refs. 9 and 10 can be used, the demodulation method of the presentinvention described later that realizes more accurate demodulation canalso be used. If the crossed beams and the corresponding spectraobtained are not symmetric with respect to the axial direction, thedemodulation is performed after the rotation of the coordinate system.

The demodulation methods generate the phases that are expressed usingthe respective displacement components, from which the respectivedisplacement components are calculated. In the demodulation of thepresent invention, when the two-dimensional displacement vector (dx,dy)is measured, the difference in the instantaneous phase at a position inthe two-dimensional ROI obtained from the two echo data frames obtainedat the two phases (time differences) are expressed using the phases ofthe analytic signals expj (fxdx+fydy) and expj (fxdx-fydy) obtained fromthe independent single quadrant spectra shown in FIG. 8b . Bycalculating the product and conjugate product of the analytic signals,the complex signals expj (2fxdx) and expj (2fydy) are obtained. Then therespective displacement vector components dx and dy can be calculated bydividing the phases of the complex signals by the respective twofoldinstantaneous frequencies 2fx and 2fy. Because the product and theconjugate product yield twofold frequency in the respective directions,the beamforming must be performed with a lateral bandwidth large enoughin advance. Otherwise, the interpolations of beams may be performed in aspatial domain or in a frequency domain, i.e., zero padding in afrequency domain.

The demodulation can also be performed for the measurement of thethree-dimensional displacement vector measurement (dx,dy,dz). At leastthe three analytic signals among the four signals expj (fxdx+fydy+fzdz),expj (fxdx+fydy−fzdz), expj (fxdx−fydy+fzdz) and expj (fxdx−fydy−fzdz)(see FIG. 1a shown in ref. 3) are used. Also in this case, the productand the conjugate product yield twofold instantaneous frequencies in therespective directions. Then, in the same manner, the beamforming must beperformed with a lateral bandwidth large enough in advance. Otherwise,the interpolations of beams may be performed in a spatial domain or in afrequency domain, i.e., zero padding in a frequency domain.

However, even if the multidimensional phase matching is performed, theresidual displacement remained leads to the measurement error. Then, themeasurement obtained using the one-dimensional displacement measurementmethods yield lower accuracy than that obtained by using thecorresponding multidimensional displacement vector measurement methods.The larger the residual displacements, the larger measurement errors areyielded. That is, the measurement errors inherent to the one-dimensionaldisplacement measurement methods occur.

Next, the multidimensional cross-spectrum phase gradient method(MCSPGM), the multidimensional autocorrelation method with a blockmatching (MAMb) and the multidimensional Doppler method with a blockmatching (MDMb) among the multidimensional displacement vectormeasurement methods that can be used for the lateral modulation can alsobe used for the beam steering with a single steering angle. A syntheticaperture can also be performed. All the methods fall in a category of ablock matching type. In conjunction, the multidimensionalcross-correlation method and SAD can also be used similarly. The beamsteering increases the measurement accuracy of the displacement vectorbecause the lateral carrier frequency can also be obtained. However, asmentioned above, the lateral modulation should be performed to yieldmore accurate measurements, because these block matching types will notyield the high accuracy for the single beam steering angle.

For the single steering angle case, the measurements of three- ortwo-dimensional displacement vector, or one-directional displacement canalso be performed by dividing the single quadrant or octant spectra, orone-dimensional spectra to yield plural analytic signals. That is, theanalytic signals obtained from the respective same bandwidths dividedfor the two echo data frames are used to derive the simultaneousequations about the unknown displacements at each position in the ROI.For the frequency division, a kind of window can also be used.Non-divided spectra can also be used together. In these cases, inaddition to the block matching types, MCSPGM, MAM, MDM and thecorresponding one-dimensional methods can also be used. The spectraaround of the ultrasound frequency and lateral frequency can be usedmainly. High or low frequency spectra can be used mainly. The spectrawith a high SNR can also be used mainly. In conjunction, the weightedsimultaneous equations can be obtained by considering the accuracy orconfidence of the corresponding spectra used (not used spectracorrespond to the condition that the weighted assigned is zero). Thenumber of equations derived should be larger than that of unknowndisplacement components. The frequency division can also be implementedon the lateral modulation. The least squares method and theregularization are implemented for solving the equations.

For the single steering angle, the following displacement measurementmethods can be used for the measurement of the one-directionaldisplacement such as a lateral or elevational displacement. A syntheticaperture may also be performed. Although the displacement of the depthdirection can also be measured using the one-directional displacementmeasurement method, the measurements of the dominant lateral andelevational displacements are performed when using the method. For thelateral displacement measurement, if the target displacement exits inthe remaining two orthogonal axes, measurement errors occur as describedlater. Then, with seeing a blood flow image (displacement or velocity),a tissue displacement image or a tissue strain image obtained using theB-mode image, the methods of the present inventions (may still have lowaccuracy at the moment) or other methods or modalities, not the beamdirection but the lateral direction is set in the direction of thetarget motion (FIG. 10). In FIG. 10, 0 expresses the steering angleconfirmed in the coordinate system finally defined. Also in this case,the above-described frequency division can be performed.

As described above, also the mechanical steering angle θm (FIG. 6) isdetected by a proper sensor. If necessary, by using a display and a penas interfaces, the angle to be corrected is detected. In order to setthe coordinate system properly at performing the beamforming or afterperforming the beamforming, the electric beam steering angle value (FIG.5) and the mechanical steering angle value to be corrected (FIG. 6) maybe indicated or displayed. The angles detected may be indicated ordisplayed in the polar coordinate system to visually confirm if theangles are proper. The indicated or displayed angles may be used toautomatically form the proper coordinate system and the proper steeredbeams through the electric beam steering or the mechanical beamsteering. A synthetic aperture may also be performed or using the sameecho data set stored. The evaluation of the angles to be corrected mayalso be automatically performed by detecting the tissue structures suchas a vessel wall in the ultrasound images or measuring the direction ofthe displacement etc. The measured displacement distribution data canalso be used. The frequency division method can also be used. Althoughthe automatic correction is desirable, the manual correction may also beperformed using the proper device such as the sensor.

Thus, for the one-directional displacement measurement achieved by usingthe following displacement measurement methods, the finally achievedproper coordinate system can be obtained by choosing an axis that is themost easily set in the direction of the target motion regardless thecoordinate system is three-, two- or one-dimensional. Then, if thetarget tissue moves in the lateral direction dominantly, not the depthaxis but the lateral axis is set in the motion direction. Such a lateralone-dimensional displacement measurement does not lead to themeasurement errors caused when using the conventional axialone-dimensional displacement measurement used under the condition thatthe beam direction cannot set in the direction of the target motion.Similarly to the lateral modulation, the configurations of thedisplacement/strain sensor and the object become simple and themeasurement accuracy achieved also becomes high.

Although the block matching method can also be used for such ameasurement, it is also possible to measure the one-directionaldisplacement (distribution, time series) by implementing the MAM or MDMon the mirror-set echo data frames obtained at two phases (differenttimes). The mirror setting can also be performed in a frequency domain.For instance, in the two-dimensional case, the setting the singlequadrant spectra at the position A or B in a mirror condition as shownin FIG. 11a realizes the mirror setting of the echo data in the axialdirection with respect to the lateral axis (FIG. 11b ) or in the lateraldirection with respect to the axial axis (FIG. 11c ). Otherwise, in aspatial domain, the mirror setting can also be performed as shown inFIGS. 11b and 11c . Basically, the mirror setting is performed locally.By superimposing the mirror-set spectra and beams on the originalspectra and beams, the quasi-lateral modulation imaging can also beperformed. The mirror setting can also be used for the three-dimensionalcase. The mirror setting can also be used for the displacementmeasurements.

With the mirror setting of steered echo data, more than the number ofindependent single quadrant (two-dimensional case) or octant(three-dimensional case) spectra required by MAM and MDM are obtained,by which independent equations more than the number of unknowndisplacements can be obtained. The mirror settings shown in FIGS. 11band 11c realized in a spatial or frequency domain are respectively usedfor the measurements of the dominant lateral and axial displacements.Because the tissue motion in the depth direction can be measured with ahigh accuracy by using conventional one-dimensional displacementmeasurement methods, the mirror setting shown in FIG. 11b is effective,particularly for the measurement of the dominant lateral displacement.Also in this case, the above described frequency division method can beused, if necessary.

Hereafter, as the one-directional displacement measurement, the dominantlateral displacement is dealt with mainly. Under the condition that thelateral axis is set in the direction of the target lateral motion (FIG.10), the mirror setting allows the measurement of the lateraldisplacement as a one-directional displacement measurement. However,only if a displacement in the axial or elevational direction exists, themeasurement errors occur. For instance, at a position in thetwo-dimensional region, the equation about the unknown two-dimensionaldisplacement vector (dx,dy) is obtained from the original singlequadrant spectra, i.e.,fxdx+fydy=c  (1)and the mirror setting derives the following equation, i.e.,−fxdx′+fydy=cwhere dx′=−dx  (1)′Moreover, c expresses the difference of the instantaneous phase betweenthe two echo signal at the position; and fx and fy are the instantaneousfrequencies in the respective directions at the position. If the axialdisplacement dx equals to zero, the equations (1) and (1)′simultaneously solved yields dx=0 and dy=c/fy under the condition thatdx′=dx. However, if dx≠0, (1)′ solved by dealing with (dx′,dy) as(dx,dy) leads to measurement errors. This is also for thethree-dimensional case. Thus, one can confirm that the proper setting ofthe coordinate system is important.

The one-directional displacement measurement has an effect on themeasurement of the dominant lateral displacement. Then, it is needlessto say that the one-directional displacement measurement method is alateral one-directional displacement measurement method. In order toobtain the measurement accuracy, the coordinate system to be final usedhas a lateral axis of which direction corresponds to that of the lateralmotion (FIG. 10), i.e., not axial axis. For instance, for themeasurement of the blood flow in thyroid as shown in FIG. 6, the lateralone-dimensional displacement measurement does not lead to themeasurement errors caused when using the conventional axialone-dimensional displacement measurement used under the condition thatthe beam direction cannot set in the direction of the target motion.Similarly to the lateral modulation (LM), the configurations of thedisplacement/strain sensor and the object become simple and themeasurement accuracy achieved also becomes high.

For the lateral one-directional displacement measurement, thedisplacement can also be measured using other above-describedone-directional displacement measurement methods such as theone-dimensional cross-spectrum phase gradient method, one-dimensionalautocorrelation method, one-dimensional Doppler method, one-dimensionalcross-correlation method, one-dimensional SAD from the MAM and MDM. Whenusing these methods, being different from the uses of the MAM and MDM,the mirror setting is not required. Also being different from thelateral modulation, the demodulation described above is not required.With these methods, the lateral displacement can be measured as c/fy.That is, the lateral displacement can be calculated by dividing thedifference of the instantaneous phase by the instantaneous lateralfrequency. Also an dominant axial displacement can also be measuredsimilarly. Also in these cases, the frequency division method describedabove can be used.

However, note that the phase matching, moving-average and block matchingshould be performed in the two- or three-dimensional region, by whichthe measurement accuracy becomes higher than the measurement using onlythe echo data on the respective one-dimensional regions (i.e., lateralones). However, these measurements cannot achieve the accuracy obtainedby the mirror setting and the corresponding multidimensionaldisplacement vector measurement methods etc.

The measurement error for the lateral displacement measurement generatedby the one-directional displacement measurement due to the displacementof the depth direction dx≠0 is expressed by −(fx/fy)×dx. Similarly tothe case using the MAM and MDM with the mirror setting, in order toobtain the high accuracy of the lateral displacement measurement, thelateral axis of the coordinate system, should be set in the direction ofthe lateral motion. However, when dx≠0, if the single quadrant spectrawith a minus axial frequency correspondingly obtained from the beamsteered in the direction of the target motion, the displacement weightedwith the instantaneous frequencies [(fx/fy)×dx+dy] is obtained as themeasurement result. If the steering angle shown in FIGS. 5a , 6 and 10is set to 45°, the summation of the displacement components [dx+dy] iscalculated because fx=fy. Such calculations are also performed for thethree-dimensional displacement vector measurement. If dx≠0 and dz≠0,(fx/fy)×dx+(fz/fy)×dz+dy is calculated as the measurement result. Whensetting the steering angle to 45°, the summation of the displacementcomponents dx+dy+dz is calculated. Also in this case, the abovefrequency division can also be performed.

Regarding the multidimensional displacement vector measurement methodsand the one-directional displacement measurement methods above-mentionedor described, the measurement accuracy can be compared. Regarding thedisplacement vector measurement, the order of the measurement accuracyevaluated by the present inventor is (LM+MAM, MDM)>(LM+MAMb, MDMb,MCSPGM)>(a single steering angle+MAMb, MDMb, MCSPGM). That is, the typeof a block matching yields a low measurement accuracy; the LM (lateralmodulation) yields a higher measurement accuracy than the single beamsteering angle. Although the combination of the demodulation method ofthe present invention and the one-directional displacement measurementmethods also allows the displacement vector measurement, the measurementaccuracy achieved is lower than the obtained by the correspondingmultidimensional displacement vector measurement methods. For the LM andthe beam steering with a single steering angle, a synthetic aperture canalso be used.

For the lateral or one-directional displacement measurement, the orderof the measurement accuracy is (a single steering angle+mirrorsetting+MAM, MDM)>(LM+MAM, MDM) or (a single steeringangle+one-directional displacement measurementmethod)>(LM+one-directional displacement measurement method).Interestingly, for the measurement of the one-directional displacement,the beam steering with a single steering angle yields a highermeasurement accuracy than the LM. The one-directional displacementmeasurement method yields a lower measurement accuracy than thecorresponding multidimensional displacement vector measurement methods.Also the type of a block matching yields a low measurement accuracy. Forthe LM and the beam steering with a single steering angle, a syntheticaperture can also be used.

Next, the quality of the beamforming is compared for the lateralmodulation and the beam steering with a single steering angle. With LM,the following properties may lead to the deterioration of measurementaccuracy:

(1) When a synthetic aperture is used for yielding plural steered beams,the ultrasound intensity transmitted from an element is small, which mayyield low SNR echo data.

(2) Alternatively, when crossed beams are superimposed, although a largeultrasound intensity can be obtained, time differences between thetransmission of the beams can cause measurement errors, if thedisplacement occurs during these time differences.

(3) Because multiple beams that have different paths are used, theinhomogeneity of tissue properties affects beamforming. Specifically,propagation speed affects focusing (i.e., the beam-crossing position),whereas attenuation and scattering lead to different frequencies of thecrossed beams.(4) At the minimum, more time is required to complete a beamforming thanthat required with ASIA. Occasionally, more time is also required tocomplete a displacement calculation than is required with ASIA.

In contrast, with the beam steering with a single steering angle, thenumber of available displacement vector measurement methods is limited.Being dependent on the measurement method, only a lateral displacementmeasurement can be performed, and any of the above concerns, points 1 to4, will not become a problem, and a simple beam forming increases theability to make real-time measurements together with higher accuracy indisplacement measurements. However, if the ultrasound intensitytransmitted from an ultrasound element is large enough, the tissuedisplacement during the echo data acquisition or the inhomogeneity ofthe tissue ultrasound properties does not become a problem, the lateralmodulation using the plural beams yields a higher echo SNR owing to thelarge number of the summation of echo signals at performing thebeamforming.

However, with LM, point (1) can be managed with new virtual sources ofthe present inventions described below. Moreover, new virtual sources ofthe present inventions described below also cope with another LMproblem: a deeply situated tissue cannot be dealt with, because a largerphysical aperture is required than that for a conventional beamforming;the vision of field (VOF) becomes narrower in the lateral andelevational directions; these problems become more sever if obstaclessuch as a bone exist in a superficial region.

A previously reported virtual source can increase the lateral spatialresolution of a B-mode image (ref. 11: C. H. Frazier et al, IEEE Trans.UFFC, vol. 45, pp. 196-207, 1998). As shown in FIG. 12a , the virtualsource is set at the focus position of an ultrasound physical aperture,an array element or a beamforming, of which lateral resolution is alsorealized in the respective depths. Since the virtual sources are set infront of the physical aperture(s), the transmission intensity form avirtual source becomes larger than that from an array element. However,the echo imaging and the displacement measurement cannot be performedaround the virtual sources and in the superficial regions in theneighborhood of the transducer.

The measurement controller 3 in the apparatus shown in FIG. 1 can setvirtual sources behind the physical array elements to increase thetransmission intensity of ultrasound (FIG. 12b ). That is, it becomespossible to transmit the ultrasounds from plural elements with respectto a virtual source set. The virtual source also allows the echo imagingand the displacement measurement in the superficial tissues.

The measurement controller 3 in the apparatus of the present invention(FIG. 1) can also set virtual receives and virtual sources as shown inrespective FIGS. 12c and 12d regardless the focus position of thephysical aperture, array elements and the beamforming. Then, a syntheticaperture can be performed with respect to the virtual sources andreceivers by finding echo signals generated by the scattering orreflection at the point of interest. The virtual sources of the presentinventions allow the extending of the VOF in all the directions.Moreover, the virtual sources of the present inventions yield anarbitrary shaped beam in an arbitrary direction regardless the geometryof the transducer aperture (FIG. 12c ). Moreover, the virtual sources ofthe present inventions can also be realized by using scatters ordiffractions set in the neighborhood of the physical acoustical sources,for instance, by putting the material including the scattered ordiffractions (FIG. 12d ). Small holes can also be used. That is, theseare dealt with as acoustical sources. The scatters in the target object(tissues etc.) can also be used as the virtual sources.

Thus, he positions of the virtual sources of the present inventions areset strictly or not (however, proper concentrations, sizes andgeometries of the scattering are required). The virtual sources of thepresent invention allow the overcoming of the limitation about thelateral resolution determined by the physical aperture size (those ofarray elements etc.). In the framework for desiring a point acousticalsource, there exist tradeoffs among the region size of the acousticalspreading, the penetration and the SNR. The tradeoffs required theoptimization of them. However, one should note that an intenseultrasound can be transmitted. A synthetic aperture can also be used.The controls of the impedance, geometry, size, position, structure,diffraction are required. Proper micro-bubbles can also be used.

For the synthetic aperture using the virtual sources, if necessary, theeffect of the attenuation of propagating sound is corrected using aweight, e.g., determined by the distance between the physical apertureand the virtual source. Regarding the weighting, a spherical wave may beassumed to be transmitted from a point acoustical source. Some finitesize aperture may also be assumed and analyzed analytically ornumerically. Otherwise, for realizing a desired point spread function(PSF), the optimization method the present inventor previously inventedcan be used to determine the above-mentioned beamforming parameters suchas the aperture size and geometry, transmission intensity (apodization)etc. for the physical and virtual sources. There is also a case wheremany small aperture (size) is used although the transmission intensityfrom an aperture becomes small. The virtual sources and receivers of thepresent invention is effective for the lateral modulation, particularly.However, the effectiveness can also be obtained on the applications forthe conventional beamformings and the beam steering with a singlesteering angle of the present invention. That is, the virtual sourcescan also be used for a real-time beamforming on the basis of the delay,phase matching and summation as well as a synthetic aperture.

In practical applications, a proper beamforming method should beselected for every organ and tissue (i.e., conventional beamformings,lateral modulation, beam steering with the single steering angleachieved by a real-time or a synthetic aperture), because every tissuehas its own motion (heart, liver etc.) and may also have obstacles suchas bones (an effective aperture size to be used may be limited). Then,the echo SNR to be achieved depends on the target and the beamformingmethods used. Being dependent on the echo SNR, the measurement accuracyincluding the spatial resolution achieved differs by the displacementmeasurement methods used (e.g., autocorrelation method, Doppler method,cross-spectrum phase gradient method etc.). When the echo SNR is high,the order of the measurement accuracy is the autocorrelationmethod>cross-spectrum phase gradient method>Doppler method; and for therespective method, the multidimensional displacement vectormeasurement>one-dimensional displacement measurement. When the echo SNRis low, the orders are inverted. The calculation speeds obtained by themeasurement methods also differ. These are specifically reported in ref.3 by the present inventor. Thus, the beamforming methods, thedisplacement measurement methods or the combinations may be selectedusing the apparatus of the present invention. Because the suitablebeamforming methods, displacement measurement methods or thecombinations can be determined for every organ and tissue, they may beautomatically selected by the apparatus of the present invention. Thefrequency division method may also be used.

Thus, the present invention supplies a new displacement measurementapparatus and a new ultrasound diagnosis apparatus having a remarkablefeature that allows the selection of the proper beamforming (e.g.,conventional beamformings, lateral modulation, beam steering with asingle steering angle and others), the proper displacement measurementmethod or the proper combination. That is, the measurement controllerand the data processing unit 1 used in the apparatuses possesses thefunction and/or method for selecting them (e.g., a manual or automaticselection).

As described above, in order to obtain a high measurement accuracy forthe lateral displacement, the beam steering angle obtained by theelectric and mechanical steering (θ in FIGS. 5, 6 and 10) is made aslarge as possible. A synthetic aperture may also be performed. Thelateral carrier frequency is made as large as possible for the echoimaging and the lateral displacement measurement. The use of an extralarge electric steering angle leads to a low echo SNR. Then, ifnecessary, the mechanical steering may also be used together with theelectric steering.

The lateral carrier frequency is tried to made as large as possible.Accordingly, on the basis of the Nyquist theorem, the beam pitch is madesmall. That is, the generation of the aliasing (FIG. 13a ) must beremoved. This is also for the lateral modulation case.

The use of the large steering angle may lead to the generations of theside lobes and grating lobes. Then, in the frequency domain, such lobesare filtered out by changing the corresponding spectra by zeros (FIG.13b ). Alternatively, by extracting the spectra, the correspondingsteering beams can be separated. Then, the signal separation can also beperformed with respect to the plural signals respectively arrived fromdifferent directions.

When it is possible to generate a large beam steering angle such thatthe higher lateral carrier frequency can be obtained than the highestfrequency determined by the Nyquist theorem, the widening of the lateralbandwidth can be performed by padding zeros in the frequencies outsidethe original lateral bandwidth, i.e., the interpolations of the lateralsampling shown in FIG. 13c . The interpolations an also be performed ina spatial domain. Otherwise, the beamforming can also be performed witha small beam pitch. When realizing plural crossed beams for the lateralmodulation, the widening of a lateral bandwidth is also effective. Asynthetic aperture may also be performed.

When the electric steering solo cannot yield a high lateral orelevational carrier frequency, the application of the mechanical scan,the coordinate system of the echo data frames can be rotated (FIG. 14a). In order to control the measurement accuracies of displacement vectorcomponents, the rotation can also be performed. The rotation can also beperformed in a frequency domain (FIG. 14b ). However, for themeasurement of a dominant lateral displacement, for instance, the bloodflow in the vessel running parallel to the body surface, the beam mustbe tried to be steered in the direction of the displacement. A syntheticaperture may also be performed.

For the purposes, a fundamental wave, or harmonic waves of which higheraxial carrier frequency and larger lateral bandwidth (narrower beam)respectively increase the measurement accuracy of the axial and lateraldisplacements, or all waves of which total single-to-noise ratio may belarger than that of the harmonic wave solo are properly used. That is,the echo imaging is performed using an ultrasound echo signal itself, afundamental wave extracted (n=1) solo, one of harmonic waves extracted(n=2 to N) solo, or combinations of them. Moreover, the measurement of adisplacement vector or a one-directional displacement (mainly, lateralone) is performed.

In the calculations, the displacement components may be obtained bysimultaneously solving the equations derived from the respective echoes.In such cases, the equations may be weighted according to the confidenceor SNR of the corresponding echoes (the least squares method orregularization may also be used). For the echo imaging, the respectivesignals corresponding to the spectra divided in a frequency domain mayalso be used, or the respective signals are superimposed afterimplementing such a weighting (signal non-used equals to the assignmentof zero to the weight). Non-divided signal may also be used together.The superimposition may be performed after implementing a detection onthe respective divided signals. Otherwise, after the superimposition ofraw rf echo signals, a detection may be implemented on the superimposedsignals. These are also for the lateral modulation or the non-steeringcase.

In these case, the data processing unit 1 may also calculate the straintensor components (distributions, time series) by implementing a 3D, 2Dor 1D spatial differential filter with a cutoff frequency in a spatialdomain or their frequency responses to the measured three- ortwo-dimensional displacement vector components (distributions, timeseries) in the three-dimensional ROI, two-dimensional displacementvector components (distributions, time series) in the two-dimensionalROI, one-directional displacement (distribution, time series) in thethree-, two- or one-dimensional ROI. The data processing unit 1 may alsocalculate the strain rate tensor components (distributions, timeseries), acceleration vector components (distributions, time series) andvelocity vector components (distributions, time series) by implementingthe temporal differential filter with a cutoff frequency or thefrequency response to the measured time series of displacements orstrains.

The measurement results can be displayed by the display unit 10 (FIG. 1)such as CRT etc., i.e., at least one of measured displacement vectorcomponents or displacement, strain tensor components or strain, strainrate tensor components or strain rate, acceleration vector components oracceleration, velocity vector components or velocity, the distribution,the time series and the corresponding B-mode image obtained byimplementing the envelope or square detection etc. For the tensors, theprincipal strain and strain rate may be respectively calculated anddisplayed similarly. If necessary, similar to the color Doppler, powerDoppler, Elastography etc., the measured distribution may be displayedusing colors in the B-mode image. Other display scheme can also be usedif the spatial resolution is yielded for the spatial position, thedirection, magnitude (intensity) etc. The vectors, principal strains andprincipal strain rates may also be displayed using a vector line map.These may be superimposed each other for the purpose of the exhibition.

Thus, the present invention supplies new methods and apparatuses(techniques) on the basis of the scanning using the steering beam with asingle steering angle. As the result, the echo data are acquired in ashorter time than by other beamformings; the error caused by the tissuemotion during the data acquisition can be significantly decreased.Moreover, by using the prescribed displacement measurement methods afterimplementing the prescribed processing on the acquired echo data, thedisplacement vector or lateral one-direction displacement can bemeasured with a considerably high accuracy. A synthetic aperture mayalso be performed. An axial one-directional displacement measurement mayalso be performed.

Moreover, by using the strain tensor distribution data calculated fromthe displacement vector distribution data measured in this conduct form,a shear modulus distribution can be calculated (for instance, see ref.12: C. Sumi, “Increasing accuracy of tissue shear modulus reconstructionusing ultrasonic strain tensor measurement—Regularization and lateralmodulation”, in Acoustical Imaging, vol. 29, pp. 59-69, Springer, 2008).When measuring the shear modulus distribution, the material of a knownshear modulus may set in the ROI as a reference. The reference region tobe realized is a region of a shear modulus absolutely or relativelyknown or estimated in advance in the reference material or in theobject. In order to measure the shear modulus distribution stably, thereference region should extend in the direction widely crossing thedirection of the dominant tissue deformation. Then, for instance, whencompressing the object using the transducer as a compressor, such areference material is put between the transducer and the object. Thereference may be assembled into the transducer itself.

The purpose of the measurements of the displacement vector distribution,strain tensor distribution and shear modulus distribution is to allownon-destructive and quantitative examinations or property evaluations ofvarious objects, structures, substances, materials, living tissues etc.For instance, when dealing with human living tissues, the compression orvibration applied externally yields the change of such mechanicalquantities and elasticity of tissues according to the lesion progress orchange of tissue characteristics. The tissue displacement or deformationcan also be dealt with by a spontaneous tissue motion such as a bodymotion, a respiratory, a heart motion, a pulsation etc. The shearmodulus value or the geometrical distribution evaluated can be used forthe differentiation of tissues (i.e., tissue characterization). Then,the display unit such as CRT described in paragraph 0111 can alsoexhibits such measured distributions as well as such values evaluated.

The methods and apparatuses can also be used for the monitoring of atreatment effectiveness or a temperature change generated by theradiotherapy such as a high intensity focus ultrasound, a leaser, anelectromagnetic radio frequency wave or a microwave etc. (see ref. 13:C. Sumi and H. Yanagimura, “Spatial inhomogeneity of tissue thermalparameter of Ebbini's model and its dependency on temperature,” Jpn JAppl Phys, vol. 46, no. 7b, pp. 4790-4792, 2007). In this case, thedisplay unit such as CRT described in paragraph 0111 can display theshear modulus calculated for the controlling the treatment before,during and after the treatment. Also the measured displacement vectordistribution, displacement vector component distributions, strain tensordistribution, strain tensor component distributions, gradientdistributions of strain tensor components, distribution of the temporalchange etc. can be display as a static or dynamic image together withthe value at an arbitrary position or the temporal change as in a graph.

By using the display function of the ultrasound image, the spatialdistributions of a bulk modulus or a density measured in a real-time canalso be displayed. As the measurement results, the displacement vectordistribution, displacement vector component distributions, strain tensordistribution, strain tensor component distributions, gradientdistributions of the strain tensor components, distributions of thetemporal change can also be displayed as a static or dynamic image. Forthe display of the displacement vector distribution measured, the vectorline map can also be used. In addition, when measuring the temperaturedistribution, the thermal properties can also be calculated for theplanning of the treatment (see ref. 13).

The methods and apparatuses can also be used for the monitoring of thetreatment effectiveness (including the temperature change), and thecontrolling and planning for the interstitial type radiotherapies suchas a high intensity focus ultrasound, a leaser, an electromagnetic radiofrequency wave or a microwave etc. In addition, the methods andapparatuses can also be used for the monitoring of the effectivenessincluding the temperature change, and the controlling and planning ofthe treatment by an anti-cancer drug.

For the monitoring of the treatment effectiveness, if a mechanicalsource cannot be used, the degeneration, dilation, shrink andtemperature change etc. can also be detected by measuring thedisplacements or strains.

In addition, the methods and apparatuses can also be used for thenon-destructive examinations for living tissues, objects, substances,materials at the growth or the producing by measuring or monitoring thedisplacement vector distribution, strain tensor distribution and shearmodulus distribution.

Thus, the present invention supplies new methods and apparatuses(techniques) on the basis of the scanning using the steering beam with asingle steering angle. As the result, the echo data are acquired in ashorter time than by other beamformings; the error caused by the tissuemotion during the data acquisition can be significantly decreased.Moreover, by using the prescribed displacement measurement methods afterimplementing the prescribed processing on the acquired echo data, thedisplacement vector or lateral one-direction displacement can bemeasured with a considerably high accuracy. A synthetic aperture mayalso be performed. An axial one-directional displacement measurement mayalso be performed. The present invention also supplies a remarkablefeature that allows the selection of the proper beamforming (e.g.,conventional beamformings, lateral modulation, beam steering with asingle steering angle and others), the proper displacement measurementmethod or the proper combination. That is, the function and/or method(i.e., a manual or automatic selection) is equipped for selecting themproperly for every organ or tissue. That is, for every organ and tissue,the best echo imaging and the best displacement measurement aresupplied. A frequency division method may also be used. When performinga synthetic aperture for the lateral modulation to be equipped together,the problems such as the low echo SNR caused due to a small ultrasoundintensity transmission from an ultrasound element, a small VOF to beobtained can be mitigated using the virtual sources or receivers of thepresent invention.

The invention claimed is:
 1. A displacement measurement apparatus comprising: at least one ultrasound sensor configured to transmit ultrasounds to an object in accordance with at least one drive signal, and detect ultrasound echo signals generated in the object to output echo signals; a driving and processing unit configured to supply the at least one drive signal to the sensor, and process the echo signals outputted from the sensor to obtain ultrasound echo data; a controller configured to control at least said driving and processing unit to yield an ultrasound echo data frame at each of plural different temporal phases based on the ultrasound echo data obtained by scanning the object using at least one ultrasound beam steered electrically and/or mechanically with at least one of (i) a single constant steering angle of 0°, (ii) a single constant non-zero steering angle, and (iii) a variable steering angle, over a three-dimensional or two-dimensional orthogonal coordinate system involving orthogonal axes in at least two of axial, lateral, and elevational directions, said ultrasound echo data frame representing a plurality of the ultrasound echo data at plural positions, said ultrasound echo data having at least one of axial, lateral, and elevational carrier frequencies and a phase generated by at least one of axial, lateral, and elevational modulations yielded based on the at least one ultrasound beam, said ultrasound echo data having one of local single octant spectra, local single quadrant spectra, and local single half-band-sided spectra in a frequency domain, and said ultrasound echo data being obtained by performing same beamforming, including at least partial spectra or corresponding complex signals, obtained by dividing or windowing one of single octant type spectra, single quadrant type spectra, and single half-band-sided type spectra in the frequency domain, and calculated with respect to the ultrasound echo data frame or at each position; and a data processing unit configured to calculate a displacement at each position or distribution thereof in at least one of the axial, lateral, and elevational directions by implementing a predetermined displacement measurement method on the ultrasound echo data yielded at the plural different temporal phases with respect to the at least one of the axial, lateral, and elevational carrier frequencies and the phase, or the one of the local single octant spectra, the local single quadrant spectra, and the local single half-band-sided spectra.
 2. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to calculate the displacement or distribution by solving simultaneous equations derived at each position from plural same bandwidth spectra or complex signals, at least one of which is obtained by using at least one ultrasound beam from original spectra or a corresponding complex signal, or a superimposition of divided spectra, windowed spectra, original spectra, or corresponding complex signals.
 3. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to calculate the displacement or distribution by solving simultaneous equations derived at each position from plural same bandwidth spectra or complex signals, at least one of which is obtained by using plural ultrasound beams from superposed spectra, or divided or windowed spectra of the superposed spectra.
 4. The displacement measurement apparatus according to claim 1, wherein said partial spectra include at least weighted spectra.
 5. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to coarsely calculate the displacement at each position or the distribution thereof by implementing a predetermined multidimensional block matching algorithm on the ultrasound echo data yielded at the plural different temporal phases, and then finely calculate the displacement at each position or the distribution thereof by implementing the predetermined displacement measurement method on the ultrasound echo data yielded at the plural different temporal phases.
 6. The displacement measurement apparatus according to claim 1, wherein said controller is configured to set at least one of virtual ultrasound sources and virtual ultrasound receivers behind or in front of a physical aperture regardless of at least one of geometry of the physical aperture and a focus position.
 7. The displacement measurement apparatus according to claim 1, further comprising at least one sensor configured to sense one selected from the group consisting of a magnetic nuclear resonance signal, electromagnetic waves, and light.
 8. The displacement measurement apparatus according to claim 1, wherein said controller is configured to change the steering angle electrically and/or mechanically to control at least one of axial, lateral, and elevational modulation frequencies so as to increase a measurement accuracy of the displacement.
 9. The displacement measurement apparatus according to claim 1, wherein said controller is configured to increase the steering angle electrically and/or mechanically to increase a carrier frequency of a direction orthogonal to the axial direction so as to increase a measurement accuracy of the displacement.
 10. The displacement measurement apparatus according to claim 1, wherein said controller is configured to steer the at least one ultrasound beam electrically and/or mechanically to make a direction of the steered beam correspond to a direction of the displacement so as to increase a measurement accuracy of the displacement.
 11. The displacement measurement apparatus according to claim 1, wherein said controller is configured to rotate the coordinate system of the ultrasound echo data frame at or after beamforming to control at least one of the axial, lateral, and elevational carrier frequencies.
 12. The displacement measurement apparatus according to claim 1, wherein said controller is configured to rotate the coordinate system of the ultrasound echo data frame at or after beamforming to obtain a high carrier frequency in a direction orthogonal to the axial direction.
 13. The displacement measurement apparatus according to claim 1, wherein said controller is configured to sense, in a case of performing the mechanical beam steering, a mechanical steering angle which is used for reforming the coordinate system by rotation of the coordinate system at or after beamforming such that a direction of one of the axes is the same as a direction of the displacement.
 14. The displacement measurement apparatus according to claim 1, wherein: said controller is configured to control at least said driving and processing unit to generate a large beam steering angle such that a higher carrier frequency in a direction orthogonal to the axial direction can be obtained than a Nyquist frequency determined by Nyquist theorem; and said data processing unit is configured to widen a bandwidth of the direction orthogonal to the axial direction by padding zeros in frequencies higher than the Nyquist frequency, or interpolate a beam pitch in a spatial domain.
 15. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to remove at least one of side lobes and grating lobes, or separate at least one of crossed ultrasound beams, waves, and plural signals arrived from arbitrary directions in a multidimensional frequency domain.
 16. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to use harmonic echo signals to derive simultaneous equations at each position for calculating one of a three-dimensional displacement vector, a two-dimensional displacement vector, and a displacement.
 17. The displacement measurement apparatus according to claim 1, wherein said data processing unit is configured to further calculate at least one of strain tensor components, a strain, strain rate tensor components, a strain rate component, acceleration vector components, an acceleration, velocity vector components, a velocity, corresponding distribution, and corresponding time series by implementing at least one of a spatial differential filter and a temporal differential filter with respect to at least one of a calculated displacement vector, a displacement, corresponding distribution, and corresponding time series.
 18. The displacement measurement apparatus according to claim 1, wherein: said data processing unit is configured to calculate at least one of displacement vector components or a displacement, strain tensor components, principal strains or a strain, strain rate tensor components, principal strain rates or a strain rate, acceleration vector components or an acceleration, velocity vector components or a velocity, corresponding distribution, and corresponding time series; and said displacement measurement apparatus further comprises a display configured to display at least one of the displacement vector components or the displacement, the strain tensor components, the principal strains or the strain, the strain rate tensor components, the principal strain rates or the strain rate, the acceleration vector components or the acceleration, the velocity vector components or the velocity, the corresponding distribution, the corresponding time series, an rf-echo image or a B-mode image obtained using at least one of divided spectra, windowed spectra, and original spectra, and an rf-echo image or a B-mode image obtained using divided or windowed spectra of a superposition of at least one of divided spectra, windowed spectra, and original spectra. 